As digital data are broadly used, various information including, for example, music, sounds and images, can be easily handled by a personal computer, a mobile computer and the like. A technique is being developed, which enables band compression of such information by an audio codec technique or a video codec technique and easy and efficient distribution of the band-compressed information to various communication terminal equipments through digital communication or digital broadcasts. For example, audio/video data (AV data) can be received outdoors by a portable telephone unit.
A transmission/reception systems for data and the like is used for various purposes, since network systems preferred at home and in a small area are proposed. Such network systems include various types of next-generation wireless systems, for example, a narrow-range radio communication system with a 5-GHz band as proposed in IEEE802.11a, a radio LAN system with a 2.45-GHz band as proposed in IEEE802.11b, and a short-range radio communication system called Bluetooth.
Using such wireless network systems effectively, the transmission/reception system can easily send/receive various data, access the Internet, and send/receive data on the Internet, in various places including home and outdoors without using a repeating installation.
In the transmission/reception system for data and the like, a communication terminal equipment which is small-sized, lightweight and portable and which has the above-described communication function must be realized. In the communication terminal equipment, modulation and demodulation of analog high-frequency signals need be carried out in a transmitting/receiving unit. Therefore, generally, a high-frequency transmitting/receiving circuit 100 based on a superheterodyne system for converting transmitting/receiving signals to an intermediate frequency, as shown in FIG. 1, is provided.
The high-frequency transmitting/receiving circuit 100 has an antenna part 101 having an antenna and a switch and adapted for receiving or transmitting information signals, and a transmission/reception switching unit 102 for switching transmission and reception. The high-frequency transmitting/receiving circuit 100 also has a receiving circuit part 105 made up of a frequency conversion circuit part 103, a demodulation circuit part 104 and the like. The high-frequency transmitting/receiving circuit 100 also has a transmitting circuit part 109 made up of a power amplifier 106, a drive amplifier 107, a modulation circuit part 108 and the like. Moreover, the high-frequency transmitting/receiving circuit 100 has a reference frequency generation circuit part for supplying a reference frequency to the receiving circuit part 105 and the transmitting circuit part 109.
Although not described in detail, the high-frequency transmitting/receiving circuit 100 constituted as described above has a large number of large-size functional components such as various filters, local oscillators (VCO) and SAW filters inserted between respective stages, and a large number of passive components such as inductors, resistors and capacitors which are proper to a high-frequency analog circuit such as a matching circuit or a bias circuit. Therefore, the high-frequency transmitting/receiving circuit 100 is large-sized as a whole and becomes an obstacle to reduction in size and weight of the communication terminal equipment.
Meanwhile, in the terminal communication equipment, a high-frequency transmitting/receiving circuit 110 based on a direct conversion system for sending and receiving information signals without performing conversion to an intermediate frequency, as shown in FIG. 2, is also used. In the high-frequency transmitting/receiving circuit 110, an information signal received by an antenna part 111 is supplied to a demodulation circuit part 113 via a transmission/reception switching unit 112 and base band processing is directly performed thereon. In the high-frequency transmitting/receiving circuit 110, an information signal generated at a source is directly modulated to a predetermined frequency band without being converted to an intermediate frequency at a modulation circuit part 114, and is then sent from the antenna part 111 via an amplifier 115 and the transmission/reception switching unit 112.
Since the high-frequency transmitting/receiving circuit 110 constituted as described above has the structure in which direct detection of an information signal is performed to send and receive the information signal without converting the information to an intermediate frequency, the number of components such as filters is reduced and the entire structure is simplified. Thus, a structure closer to one chip can be realized. However, in the high-frequency transmitting/receiving circuit 110 shown in FIG. 2, handling by a filter or a matching circuit arranged on the subsequent stage is necessary. In the high-frequency transmitting/receiving circuit 110, since amplification is carried out once on the high-frequency stage, it is difficult to realize a sufficient gain and amplification must be carried out also at a base band part. Therefore, the high-frequency transmitting/receiving circuit 110 needs a DC offset cancellation circuit and a sufficient low-pass filter. This further increases the power consumption of the whole circuit.
The conventional high-frequency transmitting/receiving circuit, whether it is based on the superheterodyne system or the direct conversion system as described above, cannot realize satisfactory characteristics to meet the requirement of reduction in size and weight of the communication terminal equipment. Therefore, various attempts have been made to constitute a module in which miniaturization is realized by using a simple structure based on, for example, a Si-CMOS circuit. Specifically, one approach is to form a passive element having good characteristics on a Si substrate, prepare a filter circuit, a resonator and the like on an LSI, and also integrate a logic LSI of a base band part, thus producing a so-called one-chip high-frequency module.
In this one-chip high-frequency module, how to form a high-performance inductor part 120 on an LSI is extremely important, as shown in FIGS. 3A and 3B. In such a one-chip high-frequency module, a large recess part 124 is formed corresponding to an inductor part forming part 123 in a Si substrate 121 and a SiO2 insulating layer 122. In the one-chip high-frequency module, a first wiring layer 125 exposed to the recess part 124 is formed and a second wiring layer 126 closing the recess part 124 is formed, thus constituting a coil part 127. In the one-chip high-frequency module, a part of the wiring pattern is raised up in the air from the substrate surface, corresponding to the other parts, thus forming the inductor part 120. For this one-chip high-frequency module, the step of forming the inductor part 120 is very complicated and the increased number of steps raises the cost.
The one-chip high-frequency module has a problem of large electrical interference of a Si substrate provided between a high-frequency circuit part of an analog circuit and a base band circuit part of a digital circuit.
As high-frequency modules which solve the foregoing problem, for example, a high-frequency module 130 using a Si substrate as a base board shown in FIG. 4 and a high-frequency module 140 using a glass substrate as a base board shown in FIG. 5 are proposed.
In the high-frequency module 130 shown in FIG. 4, a SiO2 layer 132 is formed on a Si substrate 131 and then a passive element forming layer 133 is formed thereon by a lithography technique. Although not described in detail, a wiring pattern and passive elements such as inductor parts, resistor parts or capacitor parts are formed in a multilayer form within the passive element forming layer 133 by a thin film forming technique or a thick film forming technique. In the high-frequency module 130, terminal parts connected with the internal wiring pattern through via-holes (junction through-holes) are formed on the passive element forming layer 133, and a circuit element 134 such as a high-frequency IC or LSI is directly mounted on these terminal parts by a flip-chip mounting method or the like. By mounting this high-frequency module 130, for example, on a mother board or the like, the high-frequency part and the base band circuit part are separated from each other and electrical interference between these part can be restrained. In such a high-frequency module 130, the conductive Si substrate 131 functions when forming each passive element within the passing element forming layer 133 but has a problem of hindrance to the good high-frequency characteristic of each passive element.
On the other hand, the high-frequency module 140 shown in FIG. 5 uses a glass substrate 141 as a base board in order to solve the problem of the Si substrate 131 in the above-described high-frequency module 130. Also in the high-frequency module 140, a passive element forming layer 142 is formed on the glass substrate 141 by a lithography technique. Although not described in detail, a wiring pattern and passive elements such as inductor parts, resistor parts or capacitor parts are formed in a multilayer form within the passive element forming layer 142 by a thin film forming technique or a thick film forming technique.
In the high-frequency module 140 shown in FIG. 5, terminal parts connected with the internal wiring pattern through via-holes are formed on the passive element forming layer 142, and a circuit element 143 such as a high-frequency IC or LSI is directly mounted on these terminal parts by a flip-chip mounting method or the like. Since this high-frequency module 140 uses the glass substrate 141, which is not electrically conductive, the capacitive coupling between the glass substrate 141 and the passive element forming layer 142 is restrained and passive elements having good a high-frequency characteristic can be formed within the passive element forming layer 142.
To mount the high-frequency module 140 shown in FIG. 5, for example, on a mother board or the like, a terminal pattern is formed on the surface of the passive element forming layer 142 and connection with the mother board is carried out by using a wiring bonding method or the like. The high-frequency module 140 requires a terminal pattern forming step and a wiring bonding step.
In these one-chip high-frequency modules, the passive element forming layers with high precision are formed on the base boards, as described above. In the thin film forming of the passive element forming layer, the base board requires heat resistance to a rise in surface temperature at the time of sputtering, maintenance of the depth of focus at the time of lithography, and contact alignment at the time of masking. The base board needs flatness with high accuracy, insulation property, heat resistance or chemical resistance.
The above-described Si substrate 131 and glass substrate 141 have such characteristics and enable formation of passive elements with little loss and at a low cost by a separate process from the LSI. The Si substrate 131 and the glass substrate 141 enable formation of passive elements with higher precision, compared with a pattern forming method based on printing or a wet etching method for forming a wiring pattern on a printed wiring board, used in the conventional ceramic module technique. Moreover, the Si substrate 131 and the glass substrate 141 enable reduction in area of the elements to approximately 1/100.
In these high-frequency modules, for a carrier frequency just above 5 GHz, a circuit design based on a distributed constant circuit using, for example, a transmission line coupling line stub, can realize higher performance than a circuit design based on concentrated constant elements using circuit components such as inductor parts and resistor parts. In these high-frequency modules, for higher frequencies, a design based on a distributed constant circuit is essential to the functional elements such as a band-pass filter, and the use of the concentrated constant elements such as inductor parts and resistor parts is limited to choke and decoupling.
However, in a high-frequency module 150 shown in FIG. 6, a distributed constant circuit can be formed only in one layer, that is, a passive element forming layer 151 on one major surface of the Si substrate 131 or the glass substrate 141. For example, if a band-pass filter 152 or the like is formed as a distributed constant circuit, the occupied area of the band-pass filter 152 increases. Moreover, in the high-frequency module 150, a predetermined spacing indicated by an arrow Y in FIG. 6 must be provided between the band-pass filter 152 and a mounted circuit element 153 such as a high-frequency IC or LSI, in order to avoid electrical interference. This also increases the area. The high-frequency module 150 also has a problem of increased cost due to the use of the relatively expensive Si substrate 131 or glass substrate 141.